Field of the Invention
The present invention relates to an electrostatic latent image developing toner for forming an electrophotographic image, and a process for producing the same.
Description of Related Art
An electrostatic latent image developing toner (hereinafter, also referred simply as “toner”) for forming an electrophotographic image is desired to be more excellent in low temperature fixability for saving energy for an image-forming apparatus and speeding up an image-forming process by the apparatus. Known examples of such a toner include a toner designed such that a binder resin has a lower glass transition point and a lower softening point by allowing toner particles to contain a crystalline polyester resin having a sharp-melting property as the binder resin.
However, such a toner containing the crystalline polyester resin having a lower glass transition point and a lower softening point has a problem of insufficient high-temperature storability due to easy occurrence of heat fusion of the toner particles, while such a toner has low temperature fixability. In addition, a fixed image constituted by the resin also has a problem of causing document offset due to the lower glass transition point and the lower softening point of the resin.
In order to solve these problems, a toner is proposed which is composed of toner particles in which particles are laminated on the surface of a toner base particle, the particles comprising a urethane-modified crystalline polyester resin in which a urethane polymerization segment is bonded to a polyester polymerization segment (see, e.g., Japanese Patent Application Laid-Open No. 2012-133161).
However, in the toner disclosed in PTL 1, the crystalline polyester resin component that contributes to the low temperature fixability is laminated on the surface of the toner base particle, and thus the addition amount thereof has an upper limit. Accordingly, the toner disclosed in PTL 1 has problems in which a sufficient sharp-melting property is not exerted, and further the low melting point and the low melt viscosity thereof causes aggregation and fusion of toner particles during storage of the toner, which leads to thermal aggregation of the toner, resulting in insufficient high-temperature storability.